1. Field of the Invention
The present invention relates to a form measuring machine such as a form measuring machine using a lever-type detector.
2. Description of Related Art
Nowadays, form measuring machines having lever-type detectors are in widespread use. For example, form measuring machines such as contour shape measuring machines, surface texture measuring machines, and roundness measuring machines are known.
When a crossed spring is incorporated into a rotation axis of such a lever-type detector, a measurement value with little hysteresis and high reproducibility can be obtained. However, since a measuring force changes according to a measurement position, deviation of measurement values easily occurs. Further, although measurement can be performed by low measuring force as a way to inhibit deformation of or damages to a workpiece (object to be measured), there is an issue with respect to responsiveness (a speed with which a probe follows a shape of the workpiece upon sweeping the workpiece). Measurement precision, however, does not deteriorate much by the use of low measuring force.
By contrast, a technique for stabilizing measuring force is known, in which fluctuation of the measuring force of the lever-type detector is inhibited by detecting and controlling the measuring force (see, e.g., Japanese Patent Laid-open Publication No. 2000-74616).
In addition, a technology is proposed for a measuring device using an elastic mechanism in which a restoring characteristic of an elastic hinge is adjusted using magnets (see, e.g., Japanese Patent Laid-open Publication No. H11-141537).
However, inventors of the present invention have discovered an issue, discussed below, with respect to the above-noted techniques. In the technique disclosed in Japanese Patent Laid-open Publication No. 2000-74616, controlling the measuring force generates heat, which affects the form measuring machine in the form of thermal deformation and the like and leads to a decrease in measurement precision. In addition, electrical noise is generated by executing control of the measuring force, which leads to a further decrease in measurement precision. Furthermore, a need to mount a controller on the form measuring machine increases costs of the form measuring machine.
In the technique disclosed in Japanese Patent Laid-open Publication No. H11-141537, stabilization of the measuring force is not considered in the first place; thus, the technique in its current state does not achieve stabilization of measuring force in the form measuring machine.